Hello. Thank you for having me on this beautiful night.
As BKKKPewsey said, the last played info is indeed stored in the database. However, it is stored per album, with no information (in the database) as to which song was played last.
I modified my instance of subsonic to include the time that the album was last played in addition to the date, and only show the time to admins.
The only thing I can think of, is somehow using last.fm to help you out. If you could search last.fm for the album, ordered by date played descending, you would get the proper information. Then, you might be able to integrate that into subsonic.